1. Field of Invention
This invention relates to improved submersible apparatus for generating electricity from unidirectional liquid flow and a related method. More specifically, the invention relates to an efficient, environmentally safe method of generating electrical power from the energy contained in ocean currents and river currents and the like.
2. Description of Related Art
As demand for electricity has grown with an ever increasing world population, the need for non-polluting, renewable alternative energy sources to replace fossil fuels has grown dramatically. Some of the alternative sources that have been considered and/or developed commercially during the last half of the twentieth century include those associated with wind, wave, tide, ocean current, river current, ocean thermal differential, nuclear, and geothermal energy.
The well known commercial limitations of nuclear power, geothermal power, and generation based upon differential thermal energy have eliminated these processes from consideration for greatly increased commercial application. Attention has focused on other uses, such as aerodynamic and hydrodynamic devices as means for safely and efficiently generating large quantities of electricity in the future. Such devices have generally been based upon fluid driven vaned motors caused to rotate by the force of the fluid impacting each motor vane. Efficient operation of such motors requires that resistance to rotation of the motor be minimized, the rotational speed of the motor be relatively constant over time, and the number of such motors accommodated within the device be maximized.
Devices containing one or more vaned rotating aerodynamic or hydrodynamic motors to generate electricity from fluid flow including wind and liquids such as ocean currents, river currents, and wave motion is known in the windmill and water wheel arts. The vanes in such motors may be oriented vertically or horizontally and are normally positioned radially with respect to the axis of rotation of the motor. A known means of maintaining relatively constant rotational speed and minimizing resistance to the fluid flow in such a motor is to orient each vane such that the surface area of the vane impacted by the fluid is maximized when the vane is moving in the direction of fluid flow and minimized when the vane is moving counter to the direction of fluid flow. A second known means to achieve the same end involves dividing each vane into subvanes that can be positioned to increase or decrease the surface area of the vane contacted by the fluid in response to the direction of fluid flow.
U.S. Pat. Nos. 4,551,066, 4,418,888, 4,684,817, 5,266,006, and 4,134,710, all disclose fluid-driven motors utilizing vertically oriented blades rotating about the vertical axis of the motor.
U.S. Pat. No. 4,551,066 discloses a completely submerged water wheel device having a plurality of pivotable vertical vanes circumferentially spaced around the axis of rotation of the wheel. Each vane is rotatable about its own central axis and pivots to minimize the surface area of the vane facing the incoming liquid flow when the vanes are moving counter to the direction of liquid flow and to maximize said surface area when the vanes were moving in the direction of liquid flow. Means are provided to limit the rotation of each vane to less than 360.degree..
U.S. Pat. No. 4,418,888 discloses a water wheel containing a number of vertically-oriented vanes pivotally attached to an upper and lower structure at the top and bottom, respectively, of each vane such that the outermost edge of each vane is free to rotate about the axis formed by its innermost edge. The wheel also contains controllable stops that limit the motion of each blade such that, when traveling in the upstream direction, the blades swing freely to a position parallel to the liquid flow, and when traveling in the downstream direction, the blade rests against one of the controllable stops such that the vane presents a solid surface for impact the liquid.
U.S. Pat. Nos. 4,684,817 and 5,266,006 both disclose windmills based upon an array of vertical vanes, each vane containing vertically pivotable subvanes configured such that the subvanes overlap in the closed position to provide a "solid" surface when moving in the direction of the wind and pivotally open to provide spaces through which the wind can pass in order to lower resistance when moving counter to the wind direction.
A wave-operated motor containing radially-oriented vertical vanes is disclosed in U.S. Pat. No. 4,134,710. In this device, each vertical vane is comprised of multiple horizontally-pivotable sub-vanes that close and overlap to provide a solid surface when the vane is traveling in the direction of the liquid flow and rotate around a horizontal axis to provide open areas through which the liquid can pass when the vane travels counter to the direction of liquid flow, thereby resulting in decreased resistance to rotation and increasing overall efficiency.
It is also known in the art that the efficiency of devices for converting fluid energy to electricity can be increased by employing two or more of counter-rotating motors, as taught in U.S. Pat. No. 4,174,923 which discloses a windmill having two counter-rotating aerodynamic motors for generating electrical energy.
It has also been suggested that the efficiency of fluid energy conversion devices based upon counter-rotating motors can be increased by advantageously directing the fluid flow against the vanes of each such motor, as disclosed in U.S. Pat. Nos. 4,203,702, 4,960,363, and 5,009,568, and 4,335,319.
U.S. Pat. No. 4,203,702 discloses a water-driven device wherein two vaned counter-rotating hydrodynamic turbines are caused to rotate by directing the incoming water flow against the outermost vanes of each motor. U.S. Pat. No. 4,960,363 describes a fluid flow engine in which the incoming fluid is passed through a venturi-shaped opening that is said to increase the velocity of flow prior to directing the fluid toward the innermost blades of the counter-rotating turbines in the channel formed between the two turbines.
U.S. Pat. No. 5,009,568 discloses a wave-actuated power generating device comprising multiple unidirectional rotating turbines in which a wedge-shaped wave splitter positioned at the point of liquid inlet into the generator directs a portion of each incoming wave directly against the surfaces of the turbine blades.
U.S. Pat. No. 4,335,319 describes a hydrodynamic device for generating electricity wherein the water inlet nozzle directs the liquid flow against the vertically-oriented vanes of a rotating turbine that is bordered along a portion of its circumference by a curvilinear adjacent surface which further helps to concentrate the liquid flow onto the vanes during a pre-determined arc of rotation.
In order to increase the efficiency of generating electrical power from aerodynamic and hydrodynamic devices, it is desirable to minimize the effects of variations in the velocity and direction of fluid flow entering the device and to optimize the position of the device vertically in the fluid stream.
One known method of minimizing the detrimental effect of variable velocity of liquid flow is disclosed in U.S. Pat. No. 5,191,225. It discloses an apparatus for producing electricity from wave power in which changes in water level in a chamber resulting from wave motion causes air to flow through turbines which, in turn, drive an electric generator. In order to minimize rotational speed variations in the turbines, the rotating portion of each turbine contains a massive circumferential ring that acts as a flywheel and provides a level of inertia sufficient to minimize variations in power generation due to variations in wave motion.
A method of minimizing the adverse effect of changes in direction of liquid flow on power generation is suggested in U.S. Pat. No. 5,440,176 which discloses a flexible subsea hydroelectric generating plant. It comprises several ocean current-driven turbine/generators rigidly supported from an undersea platform wherein each turbine generator can be moved vertically, horizontally, or rotated to account for variations in ocean current. Movement of the turbine/generators is controlled from a remote station located on shore or above the water surface.
Another means of optimizing location of hydrodynamically driven motors is disclosed in U.S. Pat. No. 4,850,190 which describes a system for generating thermal energy from ocean currents. A plurality of electrical generating units are suspended vertically from a fully submerged support cable. Each generating unit is pivotally mounted and includes a stabilizer that allows the unit to optimize its position relative to the incoming liquid flow. In order to minimize the forces involved in maintaining the vertical positioning of the system, the support cable and the full weight of the generating units are supported by buoyancy chambers which are anchored to the ocean floor.
Another known method of controlling the location of hydrodynamic motors submerged in river and ocean currents, disclosed in U.S. Pat. No. 4,467,218, involves tethering a vertically oriented current-driven water wheel to a vertical post anchored in the bed of the river or ocean by means of horizontal cables which prevent the motor from being swept away in the direction of current flow.
It is also known that controlled buoyancy of a fully submerged self-contained hydroelectric generating apparatus is important for proper positioning and operation, especially when the apparatus is anchored to the river or ocean bed by means of cables. In order to be of sufficient size and capacity to be effective, such hydroelectric generating units must be massive. Accordingly, the buoyancy of the unit must be closely controlled to maintain proper vertical placement and minimize the stress on the tethering cables. It is also required that the electric generator and auxiliary equipment be maintained in a sealed chamber within the unit for proper operation, as disclosed in U.S. Pat. Nos. 4,219,303, 4,163,905, and 4,163,904.
U.S. Pat. No. 4,219,303 describes a power plant for generating electricity from ocean currents anchored to the bottom of the sea by means of tether cable secured electrical generators associated therewith which are contained in water tight, air filled chambers within the structure. These chambers serve the dual function of protecting the generators from the ocean environment and contributing buoyancy to the structure. Similarly, U.S. Pat. No. 4,163,905 describes a submerged power machine in which pivotable vertical blades are connected at each end to an endless chain drivingly coupled to an electric generator contained in a flotation air compartment positioned above the compartment containing the blades. Yet another method of achieving the desired buoyancy in a hydrodynamic electric generator while enclosing the electric generator in a buoyancy chamber is disclosed in U.S. Pat. No. 4,163,904 which discloses an underwater turbine in which the fluid flow drives a turbine wheel that is circumferentially geared to an electric generator mounted within an adjacent watertight compartment.
Although the aforementioned processes and systems disclose means for generating electricity from wind, wave, and tidal energy, river flow, and ocean currents, there remains a need for a system which is capable of continuously, uniformly, and efficiently producing large quantities of electricity from the immense energy available from river and ocean currents on a commercial scale without adversely affecting commerce dependent upon such waterways and the ecosystems related thereto. A system meeting such need would greatly reduce the cost of generating electricity, lessen dependence upon dwindling supplies of fossil fuels, and reduce the negative environmental impact inherent in power generation based upon the burning of such fuels.